Power amplification module

ABSTRACT

A power amplification module includes: a first bipolar transistor in which a radio frequency signal is input to a base and an amplified signal is output from a collector; a second bipolar transistor that is thermally coupled with the first bipolar transistor and that imitates operation of the first bipolar transistor; a third bipolar transistor in which a first control voltage is supplied to a base and a first bias current is output from an emitter; a first resistor that generates a third control voltage corresponding to a collector current of the second bipolar transistor at a second terminal; and a fourth bipolar transistor in which a power supply voltage is supplied to a collector, the third control voltage is supplied to a base, and a second bias current is output from an emitter.

This is a continuation of U.S. patent application Ser. No. 15/372,510filed on Dec. 8, 2016, which is a continuation of U.S. patentapplication Ser. No. 15/184,035 filed on Jun. 16, 2016, which claimspriority from Japanese Patent Application No. 2015-141429 filed on Jul.15, 2015. The contents of these applications are incorporated herein byreference in their entireties.

BACKGROUND

The present disclosure relates to a power amplification module.

The second generation mobile communication system (2G) and thethird/fourth generation mobile communication system (3G/4G) are examplesof wireless communication schemes used in mobile terminals. In 2G, it isrequired that the power of a radio frequency (RF) signal be changed inaccordance with the waveform characteristics, which are stipulated bythe standard, at the time of a burst operation in which data iscontinuously transmitted from a mobile terminal. In addition, a poweramplification module, which is for amplifying the power of an RF signal,is used in a mobile terminal in order to transmit the RF signal to abase station. Therefore, it is required that gain variations besuppressed in the power amplification module in order to output an RFsignal in accordance with the waveform characteristics stipulated by thestandard.

For example, a radio frequency amplifier that aims to suppress gainvariations that occur with changes in temperature is disclosed in FIG. 3of Japanese Unexamined Patent Application Publication No. 11-330866.This radio frequency amplifier includes a power transistor Q1 and acontrol transistor Qc having a size of 1/m of that of the powertransistor Q1. An RF signal input to the base of the power transistor Q1is input to the base of the control transistor Qc via a resistor Rb/mand a resistor Rb. Changes that occur in the collector current of thepower transistor Q1 with changes in temperature and so forth arereflected in the collector current of the control transistor Qc. A biascurrent supplied to the base of the power transistor Q1 is controlledand gain variations are suppressed by controlling a differentialamplifier in accordance with changes in the collector current of thecontrol transistor Qc.

As described above, the bias current is controlled by using adifferential amplifier in order to suppress gain variations that occurwith changes in temperature in the configuration disclosed in JapaneseUnexamined Patent Application Publication No. 11-330866. Consequently,the circuit scale is increased.

BRIEF SUMMARY

The present disclosure provides a power amplification module that cansuppress gain variations that occur with changes in temperature withoutnecessarily increasing the circuit scale.

A power amplification module according to an embodiment of the presentdisclosure includes: a first bipolar transistor that has a radiofrequency signal input to a base thereof and that outputs from acollector thereof an amplified signal obtained by amplifying the radiofrequency signal; a second bipolar transistor that is thermally coupledwith the first bipolar transistor, that has the radio frequency signalinput to a base thereof, and that imitates operation of the firstbipolar transistor; a third bipolar transistor that has a power supplyvoltage supplied to a collector thereof, that has a first controlvoltage supplied to a base thereof and that outputs a first bias currentfrom an emitter thereof to the bases of the first and second bipolartransistors; a first resistor that has a second control voltage suppliedto a first terminal thereof, that has a second terminal thereofconnected to a collector of the second bipolar transistor and thatgenerates a third control voltage at the second terminal thereof, thethird control voltage corresponding to a collector current of the secondbipolar transistor; and a fourth bipolar transistor that has the powersupply voltage supplied to a collector thereof, that has the thirdcontrol voltage supplied to a base thereof and that outputs a secondbias current from an emitter thereof to the bases of the first andsecond bipolar transistors.

According to the embodiment of the present disclosure, a poweramplification module can be provided that can suppress gain variationsthat that occur with changes in temperature and that can suppress anincrease in circuit scale.

Other features, elements, characteristics and advantages of the presentdisclosure will become more apparent from the following detaileddescription of embodiments of the present disclosure with reference tothe attached drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 illustrates an example configuration of a transmission unit thatincludes a power amplification module according to an embodiment of thepresent disclosure;

FIG. 2 illustrates an example configuration of the power amplificationmodule;

FIG. 3 illustrates configurations of an amplification circuit and a biascircuit, which are example configurations of the amplification circuitand the bias circuit illustrated in FIG. 2;

FIG. 4 illustrates the configuration of a comparative example, which isfor comparison with the embodiment;

FIG. 5 illustrates simulation results for the comparative exampleillustrated in FIG. 4;

FIG. 6 illustrates simulation results for the amplification circuit andthe bias circuit of the embodiment;

FIG. 7 illustrates configurations of an amplification circuit and a biascircuit, which are example configurations of the amplification circuitand the bias circuit illustrated in FIG. 2;

FIG. 8 illustrates configurations of an amplification circuit and a biascircuit, which are example configurations of the amplification circuitand the bias circuit illustrated in FIG. 2; and

FIG. 9 illustrates configurations of an amplification circuit and a biascircuit, which are example configurations of the amplification circuitand the bias circuit illustrated in FIG. 2.

DETAILED DESCRIPTION

Hereafter, embodiments of the present disclosure will be described whilereferring to the drawings. FIG. 1 illustrates an example configurationof a transmission unit that includes a power amplification moduleaccording to an embodiment of the present disclosure. A transmissionunit 100 is for example used in a mobile communication device such as acellular phone in order to transmit various signals such as speech anddata to a base station. Although such a mobile communication devicewould also be equipped with a reception unit for receiving signals fromthe base station, the description of such a reception unit is omittedhere.

As illustrated in FIG. 1, the transmission unit 100 includes a base bandunit 110, an RF unit 111, a power amplification module 112, a front endunit 113 and an antenna 114.

The base band unit 110 modulates an input signal such as speech or dataand outputs a modulated signal. In this embodiment, the modulated signaloutput from the base band unit 110 is output as IQ signals (I signal andQ signal) with the amplitude and the phase being represented on an IQplane. The frequencies of the IQ signals are on the order of several MHzto several tens of MHz, for example. In addition, the base band unit 110outputs a mode signal MODE that is for controlling the gain in the poweramplification module 112.

The RF unit 111 generates an RF signal (RF_(IN)), which is forperforming wireless transmission, from the IQ signals output from thebase band unit 110. The RF signal has a frequency of around severalhundred MHz to several GHz, for example. In the RF unit 111, the IQsignals may be converted into an intermediate frequency (IF) signal andan RF signal may be then generated from the IF signal, instead ofdirectly converting the IQ signals into the RF signal.

The power amplification module 112 amplifies the power of the RF signal(RF_(IN)) output from the RF unit 111 up to the level that is requiredto transmit the RF signal to the base station, and outputs an amplifiedsignal (RF_(OUT)). In the power amplification module 112, the size of abias current is determined and the gain is controlled on the basis ofthe mode signal MODE supplied from the base band unit 110.

The front end unit 113 performs filtering on the amplified signal(RF_(OUT)) and switching on a reception signal received from the basestation. The amplified signal output from the front end unit 113 istransmitted to the base station via the antenna 114.

FIG. 2 illustrates an example configuration of the power amplificationmodule 112. As illustrated in FIG. 2, the power amplification module 112includes an amplification circuit 200, an inductor 210, a bias controlcircuit 220 and a bias circuit 230.

The amplification circuit 200 amplifies the RF signal (RF_(IN)) andoutputs an amplified signal (RF_(OUT)). The number of stages of theamplification circuit is not limited to one and may be two or more.

The inductor 210 is provided in order to isolate the RF signal. A powersupply voltage V_(CC) is supplied to the amplification circuit 200 viathe inductor 210.

The bias control circuit 220 outputs control voltages V₁ and V₂, whichare for controlling a bias current I_(BIAS), on the basis of the modesignal MODE.

The bias circuit 230 supplies the bias current I_(BIAS) to theamplification circuit 200. The size of the bias current output from thebias circuit 230 is controlled by the control voltages V₁ and V₂.

FIG. 3 illustrates configurations of an amplification circuit 200A and abias circuit 230A, which are example configurations of the amplificationcircuit 200 and the bias circuit 230 illustrated in FIG. 2.

The amplification circuit 200A includes a bipolar transistor 300, acapacitor 301 and a resistor 302. The bipolar transistor 300 (firstbipolar transistor) is a heterojunction bipolar transistor (HBT), forexample. The RF signal (RF_(IN)) is input to the base of the bipolartransistor 300 via the capacitor 301. The power supply voltage V_(CC) issupplied to the collector of the bipolar transistor 300 via the inductor210. The emitter of the bipolar transistor 300 is grounded. In addition,the bias current is supplied to the base of the bipolar transistor 300via the resistor 302 (second resistor). The amplified signal (RF_(OUT))is output from the collector of the bipolar transistor 300.

The bias circuit 230A includes bipolar transistors 310, 311, 312, 313and 314, capacitors 320 and 321 and resistors 330, 331, 332 and 333. Thebipolar transistors 310 to 314 are HBTs, for example.

The bipolar transistor 310 (second bipolar transistor) is a transistorthat imitates operation of the bipolar transistor 300. The RF signal(RF_(IN)) is input to the base of the bipolar transistor 310 via thecapacitor 320. The collector of the bipolar transistor 310 is connectedto the resistor 332. The emitter of the bipolar transistor 310 isgrounded. In addition, the bias current is supplied to the base of thebipolar transistor 310 via the resistor 330 (third resistor). Anamplified signal obtained by amplifying the RF signal (RF_(IN)) isoutput from the collector of the bipolar transistor 310. In other words,the collector current of the bipolar transistor 310 is at a level thatcorresponds to the RF signal (RF_(IN)).

The emitter area of the bipolar transistor 310 may be smaller than theemitter area of the bipolar transistor 300. Consumption of current inthe bias circuit 230A can be reduced by making the emitter area of thebipolar transistor 310 smaller.

The control voltage V₂ (second control voltage) is supplied to a firstterminal of the resistor 332 (first resistor) and a second terminal ofthe resistor 332 is connected to the collector of the bipolar transistor310. The collector current of the bipolar transistor 310 flows to theresistor 332. Thus, a control voltage V₃ (third control voltage) thatcorresponds to the collector current of the bipolar transistor 310 isgenerated at the second terminal of the resistor 332.

The bipolar transistor 311 (third bipolar transistor) is a transistorfor generating a bias current (first bias current) to be supplied to thebipolar transistors 300 and 310. A power supply voltage (for example,battery voltage V_(BAT)) is supplied to the collector of the bipolartransistor 311. The base of the bipolar transistor 311 is connected tothe base of the bipolar transistor 313. A control voltage V₄ (firstcontrol voltage), which is for controlling the bias current, is suppliedto the base of the bipolar transistor 311. The emitter of the bipolartransistor 311 is connected to the resistors 302 and 330. A bias current(first bias current) that corresponds to the control voltage V₄ isoutput from the emitter of the bipolar transistor 311.

The bipolar transistor 312 (fourth bipolar transistor) is a transistorfor generating a bias current (second bias current) to be supplied tothe bipolar transistors 300 and 310. A power supply voltage (forexample, battery voltage V_(BAT)) is supplied to the collector of thebipolar transistor 312. The base of the bipolar transistor 312 isconnected to a first terminal of the resistor 333. A second terminal ofthe resistor 333 is connected to the second terminal of the resistor332. Therefore, the control voltage V₃ (third control voltage)(actually, a voltage that is lower than the control voltage V₃ by anamount corresponding to the base current of bipolar transistor 312) issupplied to the base of the bipolar transistor 312 via the resistor 333.The emitter of the bipolar transistor 312 is connected to the resistors302 and 330. A bias current (second bias current) that corresponds tothe control voltage V₃ is output from the emitter of the bipolartransistor 312.

The control voltage V₁ (fourth control voltage) is supplied to a firstterminal of the resistor 331 (fifth resistor) and a second terminal ofthe resistor 331 is connected to the collector of the bipolar transistor313.

The base and the collector of the bipolar transistor 313 (fifth bipolartransistor) are connected to each other, the base of the bipolartransistor 313 is connected to the base of the bipolar transistor 311,and the emitter of the bipolar transistor 313 is connected to thecollector of the bipolar transistor 314 (sixth bipolar transistor). Thebase and the collector of the bipolar transistor 314 are connected toeach other and the emitter of the bipolar transistor 314 is grounded.The control voltage V₄ corresponding to the control voltage V₁ is outputfrom the base of the bipolar transistor 313.

A first terminal of the capacitor 321 is connected to the base of thebipolar transistor 313 and a second terminal of the capacitor 321 isgrounded.

The bipolar transistors 300, 310 and 314 are thermally coupled with eachother in the amplification circuit 200A and the bias circuit 230A. Inother words, the bipolar transistors 300, 310 and 314 are arranged closeto each other on an integrated circuit such that when the temperature ofone transistor varies, the temperatures of the other transistors alsovary.

Operation of the amplification circuit 200A and the bias circuit 230Awill be described next.

The gain of the amplification circuit 200A changes when the temperatureof the bipolar transistor 300 changes due to the operation of thebipolar transistor 300. Specifically, when the temperature changes, thecommon-emitter current amplification factor (hereafter, simply “currentamplification factor”) β and the base-emitter voltage V_(BE) change. Thecurrent amplification factor β and the base-emitter voltage V_(BE) bothdecrease as the temperature increases. Assuming that the base voltageand the collector voltage of the bipolar transistor 300 are constant, adecrease in the current amplification factor β causes an idling currentto decrease. In addition, a decrease in the base-emitter voltage V_(BE)causes the idling current to increase. Here, the current amplificationfactor β and the base-emitter voltage V_(BE) contribute differentamounts to the idling current and therefore the gain of theamplification circuit 200A varies with changes in the currentamplification factor β and the base-emitter voltage V_(BE).

For example, if it is assumed that the bias current I_(BIAS) isconstant, the gain of the amplification circuit 200A decreases when thecurrent amplification factor β of the bipolar transistor 300 decreasesdue to an increase in temperature. At this time, since the bipolartransistor 310 imitates the operation of the bipolar transistor 300, thebipolar transistor 310 undergoes a similar change in temperature to thebipolar transistor 300. Therefore, the current amplification factor β ofthe bipolar transistor 310 decreases and the control voltage V₃increases. When the control voltage V₃ increases, the bias currentoutput from the emitter of the bipolar transistor 312 increases. Thus,the bias current I_(BIAS) supplied to the bipolar transistor 300increases and a decrease in the gain of the amplification circuit 200Ais suppressed.

Since the bipolar transistors 300 and 310 are thermally coupled witheach other in the amplification circuit 200A and the bias circuit 230A,changes in the current amplification factor β that occur with changes intemperature can be more accurately connected to each other.

Furthermore, for example, if it assumed that the bias current isconstant, the gain of the amplification circuit 200A increases when thebase-emitter voltage V_(BE) of the bipolar transistor 300 decreases dueto an increase in temperature. The bipolar transistors 300 and 314 arethermally coupled with each other in the amplification circuit 200A andthe bias circuit 230A. Therefore, the bipolar transistor 314 undergoes asimilar change in temperature to the bipolar transistor 300. Therefore,the base-emitter voltage V_(BE) of the bipolar transistor 314 decreasesand the control voltage V₄ decreases. When the control voltage V₄decreases, the bias current output from the emitter of the bipolartransistor 311 decreases. Thus, the bias current I_(BIAS) supplied tothe bipolar transistor 300 decreases and an increase in the gain of theamplification circuit 200A is suppressed.

Thus, variations in gain caused by changes in the temperature of thebipolar transistor 300 can be suppressed in the amplification circuit200A and the bias circuit 230A. In addition, by configuring the biascircuit 230A to control the bias current, an increase in circuit scaleis reduced compared with the case where a differential amplifier isused.

Furthermore, in the amplification circuit 200A, the RF signal (RF_(IN))is supplied to a point between the resistor 302 and the base of thebipolar transistor 300 via the capacitor 301. Similarly, in the biascircuit 230A, the RF signal (RF_(IN)) is supplied to a point between theresistor 330 and the base of the bipolar transistor 310 via thecapacitor 320. Thus, the path along which the RF signal (RF_(IN)) issupplied to the bipolar transistor 310 is the same as the path alongwhich the RF signal (RF_(IN)) is supplied to the bipolar transistor 300.For example, if there were a resistor on the path along which the RFsignal (RF_(IN)) is supplied to the bipolar transistor 310, analternating-current component of the RF signal (RF_(IN)) would beattenuated and the accuracy with which the bipolar transistor 310imitates the bipolar transistor 300 would decrease. In the configurationillustrated in FIG. 3, the RF signal (RF_(IN)) is supplied along thesame path to the bipolar transistors 300 and 310 and therefore adecrease in the imitation accuracy of the bipolar transistor 310 can beprevented. Thus, the effect of suppressing variations in gain that occurwith changes in temperature is improved.

The suppression of variations in gain that occur with changes in thecurrent amplification factor β in the amplification circuit 200A and thebias circuit 230A of this embodiment will be described by usingsimulation results. FIG. 4 illustrates the configuration of acomparative example, which is for comparison with this embodiment. Thecomparative example includes the amplification circuit 200A and a biascircuit 400. Elements that are the same as those illustrated in FIG. 3are denoted by the same symbols and description thereof is omitted.

As illustrated in FIG. 4, the bias circuit 400 includes the bipolartransistors 311, 313 and 314, a capacitor 321 and a resistor 331. Thebias circuit 400 does not include the bipolar transistors 310 and 312,the capacitor 320 and the resistors 330, 332 and 333 of the bias circuit230A. In other words, the bias circuit 400 does not include a part thatsuppresses gain variations of the amplification circuit 200A caused bychanges in the current amplification factor β that occur with changes inthe temperature of the bipolar transistor 300. In addition, the bipolartransistors 300 and 314 are thermally coupled with each other.

FIG. 5 illustrates simulation results for the comparative exampleillustrated in FIG. 4. In FIG. 5, the horizontal axis represents time(seconds) and the vertical axis represents output power (dBm). Thevertical axis is normalized such that a target level of the output poweris zero. A target level, an upper limit and a lower limit of the outputpower are illustrated in FIG. 5. FIG. 5 illustrates results obtained byoutputting a pulse signal such that the output power comes to be at thetarget level. In the results illustrated in FIG. 5, in particular, thegain varies in a period of around 200 microseconds after the start ofoperation.

FIG. 6 illustrates simulation results for the amplification circuit 200Aand the bias circuit 230A of this embodiment. The horizontal axis andthe vertical axis represent the same variables as in FIG. 5. FIG. 6illustrates results obtained by outputting a pulse signal such that theoutput power comes to be at the target level, similarly to as in FIG. 5.In the results illustrated in FIG. 6, in particular, it is clear thatthe size of the variation in gain is reduced in the period of around 200microseconds after the start of operation when compared with the resultsillustrated in FIG. 5. Thus, it is also clear from these simulationresults that the variations in gain that occur with changes in thecurrent amplification factor β are suppressed in the amplificationcircuit 200A and the bias circuit 230A of this embodiment.

FIG. 7 illustrates the configurations of an amplification circuit 200Band a bias circuit 230B, which are example configurations of theamplification circuit 200 and the bias circuit 230. Elements that arethe same as those of the amplification circuit 200A and the bias circuit230A illustrated in FIG. 3 are denoted by the same symbols anddescription thereof is omitted.

The amplification circuit 200B does not include the capacitor 301 andthe resistor 302 of the amplification circuit 200A illustrated in FIG.3. The bias circuit 230B does not include the capacitor 320 of the biascircuit 230A illustrated in FIG. 3. The RF signal (RF_(IN)) is input tothe bases of the bipolar transistors 300 and 310 via a capacitor 700. Inaddition, a first terminal of the resistor 330 (fourth resistor) isconnected to the emitters of the bipolar transistors 311 and 312 and asecond terminal of the resistor 330 is connected to the bases of thebipolar transistors 300 and 310. In other words, in the configurationillustrated in FIG. 7, the capacitor 700 and the resistor 330 are sharedby the amplification circuit 200B and the bias circuit 230B. With thisconfiguration as well, the same effect as with the configurationillustrated in FIG. 3 can be attained. Furthermore, the circuit scale ofthe power amplification module 112 can be reduced as result of thecapacitor 700 and the resistor 330 being shared.

FIG. 8 illustrates the configurations of the amplification circuit 200Aand a bias circuit 230C, which are example configurations of theamplification circuit 200 and the bias circuit 230. Elements that arethe same as those of the amplification circuit 200A and the bias circuit230A illustrated in FIG. 3 are denoted by the same symbols anddescription thereof is omitted.

The bias circuit 230C includes a bipolar transistor 800 and a resistor810 in addition to the elements included in the bias circuit 230Aillustrated in FIG. 3. The bipolar transistor 800 is an HBT, forexample. The collector of the bipolar transistor 800 (seventh bipolartransistor) is connected to the emitters of the bipolar transistors 311and 312, the base of the bipolar transistor 800 is connected to the baseof the bipolar transistor 314 via the resistor 810 (sixth resistor) andthe emitter of the bipolar transistor 800 is grounded. The bipolartransistor 800 is thermally coupled with the bipolar transistor 300.

With the configuration illustrated in FIG. 8, degradation of thelinearity of the power amplification module 112 can be suppressed byproviding the bipolar transistor 800 in the bias circuit 230C. This willbe explained below.

In the bias circuit 230C, a bias current is output from the emitters ofthe bipolar transistors 311 and 312. Here, the bias current exhibitsamplitude variations due to the effect of the RF signal (RF_(IN)). Whenthe level of the RF signal (RF_(IN)) becomes large, the amplitude of thebias current also becomes large. When the amplitude of the bias currentbecomes large, a negative current (current in direction from resistors302 and 330 toward emitters of bipolar transistors 311 and 312) isgenerated.

The negative current might be cut by the rectification action of thebase-emitter PN junctions of the bipolar transistors 311 and 312 in thecase of a configuration that does not include the bipolar transistor 800(in other words, bias circuit 230A illustrated in FIG. 3). When thenegative current is cut, the average bias current increases and the gainof the amplification circuit 200A becomes larger. The increase in thegain of the amplification circuit 200A leads to a decrease in thelinearity of the power amplification module 112.

In the bias circuit 230C, the negative current flows to ground via thebipolar transistor 800. Therefore, since the negative part of the biascurrent is not cut in the bias circuit 230C, an increase in the averagebias current in the case where the level of the RF signal (RF_(IN))becomes large can be suppressed. Thus, degradation of the linearity ofthe gain in the power amplification module 112 can be suppressed.

Thus, in addition to achieving the same effect as with the configurationillustrated in FIG. 3, degradation of the linearity of the gain in thepower amplification module 112 can be suppressed with the configurationillustrated in FIG. 8.

Furthermore, the resistor 810 is provided between the base of thebipolar transistor 314 and the base of the bipolar transistor 800 in theconfiguration illustrated in FIG. 8. As a result, the size of thecurrent that flows to the bipolar transistor 800 can be adjusted.

In addition, the bipolar transistor 800 is thermally coupled with thebipolar transistor 300 in the configuration illustrated in FIG. 8. As aresult, the size of the current that flows to the bipolar transistor 800is adjusted with changes in the temperature of the bipolar transistor800.

A configuration similar to that illustrated in FIG. 8 can be adopted forthe configuration illustrated in FIG. 7 as well.

FIG. 9 illustrates configurations of the amplification circuit 200A anda bias circuit 230D, which are example configurations of theamplification circuit 200 and the bias circuit 230. Elements that arethe same as those of the amplification circuit 200A and the bias circuit230A illustrated in FIG. 3 are denoted by the same symbols anddescription thereof is omitted.

The bias circuit 230D includes field effect transistors (FETs) 900, 901and 902 instead of the bipolar transistors 311, 312 and 313 of the biascircuit 230A.

The battery voltage V_(BAT) is supplied to the drain of the FET 900(first field effect transistor). The gate of the FET 900 is connected tothe gate of the FET 902. The control voltage V₄ is supplied to the gateof the FET 900. The source of the FET 900 is connected to the resistors302 and 330.

The battery voltage V_(BAT) is supplied to the drain of the FET 901(second field effect transistor). The gate of the FET 901 is connectedto the first terminal of the resistor 333. The second terminal of theresistor 333 is connected to the second terminal of the resistor 332.Therefore, the control voltage V₃ (actually, a voltage that is lowerthan the control voltage V₃ by an amount corresponding to the gatecurrent of the FET 901) is supplied to the gate of the FET 901 via theresistor 333. The source of the FET 901 is connected to the resistors302 and 330.

The drain of the FET 902 (third field effect transistor) is connected tothe second terminal of the resistor 331. The gate and the drain of theFET 902 are connected to each other, the gate of the FET 902 isconnected to the gate of the FET 900 and the source of the FET 902 isconnected to the collector of the bipolar transistor 314. The controlvoltage V₄ corresponding to the control voltage V₁ is output from thegate of the FET 902.

In the bias circuit 230D, the FETs 900, 901 and 902 operate in the sameways as the bipolar transistors 311, 312 and 313 of the bias circuit230A. Thus, the same effect can be achieved with the bias circuit 230Das with the bias circuit 230A. In addition, in the bias circuit 230D, asa result of using the FETs 900, 901 and 902, lower voltage operation ispossible compared with the case where the bipolar transistors 311, 312and 313 are used.

The FETs 900, 901 and 902 may be provided instead of the bipolartransistors 311, 312 and 313 in the bias circuit 230B illustrated inFIG. 7 and the bias circuit 230C illustrated in FIG. 8 as well.

Exemplary embodiments of the present disclosure have been describedabove. In the configuration illustrated in FIG. 3, the bias currentoutput from the bipolar transistor 312 is controlled in accordance withthe collector current of the bipolar transistor 310 that imitates theoperation of the bipolar transistor 300. Thus, variations in gain causedby changes in the temperature of the bipolar transistor 300 can besuppressed. Furthermore, since a differential amplifier is not needed asa part for controlling the bias current in the bias circuit 230A, anincrease in circuit scale can be suppressed. The same is true for theconfigurations illustrated in FIGS. 7 to 9 as well.

In addition, in the configuration illustrated in FIG. 3, since thebipolar transistors 300 and 310 are thermally coupled with each other,the accuracy with which the bipolar transistor 310 imitates theoperation of the bipolar transistor 300 is improved and the effect ofsuppressing variations in gain caused by changes in the temperature ofthe bipolar transistor 300 is improved. The same is true for theconfigurations illustrated in FIGS. 7 to 9 as well.

Furthermore, in the configuration illustrated in FIG. 3, the emitterarea of the bipolar transistor 310 that imitates the operation of thebipolar transistor 300 is smaller than the emitter area of the bipolartransistor 300. Therefore, the current consumption can be reduced. Thesame is true for the configurations illustrated in FIGS. 7 to 9 as well.

In addition, in the configuration illustrated in FIG. 3, the path alongwhich the RF signal (RF_(IN)) is supplied to the bipolar transistor 310is the same as the path along which the RF signal (RF_(IN)) is suppliedto the bipolar transistor 300. Thus, a reduction in the imitationaccuracy of the bipolar transistor 310 is prevented and the effect ofsuppressing variations in gain caused by changes in temperature isimproved. The same is true for the configurations illustrated in FIGS. 7to 9 as well.

In addition, the bipolar transistor 314 is thermally coupled with thebipolar transistor 300 in the configuration illustrated in FIG. 3.Therefore, the base-emitter voltage V_(BE) of the bipolar transistor 314changes with the base-emitter voltage V_(BE) of the bipolar transistor300. The control voltage V₄ supplied to the base of the bipolartransistor 311 changes in conjunction with changes in the base-emittervoltage V_(BE) of the bipolar transistor 314, and consequently the biascurrent output from the bipolar transistor 311 changes. Thus, variationsin gain caused by changes in the temperature of the bipolar transistor300 can be suppressed. The same is true for the configurationsillustrated in FIGS. 7 to 9 as well.

Furthermore, in the configuration illustrated in FIG. 8, a negativecurrent generated when the level of the RF signal (RF_(IN)) becomeslarge (current in direction from resistors 302 and 330 toward emittersof bipolar transistor 311 and 312) flows to ground via the bipolartransistor 800. Therefore, an increase in the average bias current issuppressed and degradation of the linearity of the gain in the poweramplification module 112 can be suppressed.

In addition, the resistor 810 is provided between the base of thebipolar transistor 314 and the base of the bipolar transistor 800 in theconfiguration illustrated in FIG. 8. As a result, the size of thecurrent that flows to the bipolar transistor 800 can be adjusted.

Furthermore, the bipolar transistor 800 is thermally coupled with thebipolar transistor 300 in the configuration illustrated in FIG. 8. As aresult, the size of the current that flows to the bipolar transistor 800is adjusted with changes in the temperature of the bipolar transistor800.

In addition, in the configuration illustrated in FIG. 9, the FETs 900,901 and 902 are provided instead of the bipolar transistors 311, 312 and313 in the configuration illustrated in FIG. 3. Thus, lower voltageoperation is possible compared with the case where the bipolartransistors 311, 312 and 313 are used.

The purpose of the embodiments described above is to enable easyunderstanding of the present disclosure and the embodiments are not tobe interpreted as limiting the present disclosure. The presentdisclosure can be modified or improved without departing from the gistof the disclosure and equivalents to the present disclosure are alsoincluded in the present disclosure. In other words, appropriate designchanges made to the embodiments by one skilled in the art are includedin the scope of the present disclosure so long as the changes have thecharacteristics of the present disclosure. For example, the elementsincluded in the embodiments and the arrangements, materials, conditions,shapes, sizes and so forth of the elements are not limited to thoseexemplified in the embodiments and can be appropriately changed. Inaddition, the elements included in the embodiments can be combined asmuch as technically possible and such combined elements are alsoincluded in the scope of the present disclosure so long as the combinedelements have the characteristics of the present disclosure.

While embodiments of the disclosure have been described above, it is tobe understood that variations and modifications will be apparent tothose skilled in the art without departing from the scope and spirit ofthe disclosure. The scope of the disclosure, therefore, is to bedetermined solely by the following claims.

What is claimed is:
 1. A power amplification module comprising: a firstbipolar transistor, wherein a radio frequency signal is input to a baseof the first bipolar transistor, and an amplified signal obtained byamplifying the radio frequency signal is output from a collector of thefirst bipolar transistor; a second bipolar transistor that imitatesoperation of the first bipolar transistor when the radio frequencysignal is input to a base of the second bipolar transistor; a thirdbipolar transistor, wherein a power supply voltage is supplied to acollector of the third bipolar transistor, a first control voltage issupplied to a base of the third bipolar transistor, and a first biascurrent is output from an emitter of the third bipolar transistor to thebase of the first bipolar transistor and the base of the second bipolartransistor; and a first resistor, wherein a second control voltage issupplied to a first end of the first resistor, a second end of the firstresistor is connected to a collector of the second bipolar transistor,and the first resistor generates a third control voltage at the secondend of the first resistor, the third control voltage corresponding to acollector current of the second bipolar transistor.
 2. The poweramplification module according to claim 1, wherein an emitter area ofthe second bipolar transistor is smaller than an emitter area of thefirst bipolar transistor.
 3. The power amplification module according toclaim 1, further comprising: a second resistor, wherein a first end ofthe second resistor is connected to the emitter of the third bipolartransistor, and a second end of the second resistor is connected to thebase of the first bipolar transistor; and a third resistor, wherein afirst end of the third resistor is connected to the emitter of the thirdbipolar transistor, and a second end of the third resistor is connectedto the base of the second bipolar transistor, wherein the radiofrequency signal is supplied to a node between the second end of thesecond resistor and the base of the first bipolar transistor, and to anode between the second end of the third resistor and the base of thesecond bipolar transistor.
 4. The power amplification module accordingto claim 1, further comprising: a fourth resistor, wherein a first endof the fourth resistor is connected to the emitter of the third bipolartransistor, and a second end of the fourth resistor is connected to thebase of the first bipolar transistor and the base of the second bipolartransistor; wherein the radio frequency signal is supplied to a nodebetween the second end of the fourth resistor, the base of the firstbipolar transistor, and the base of the second bipolar transistor. 5.The power amplification module according to claim 4, further comprising:a first capacitor, wherein the radio frequency signal is input to thebase of the first bipolar transistor and the base of the second bipolartransistor via the first capacitor.
 6. A power amplification modulecomprising: a first bipolar transistor, wherein a radio frequency signalis input to a base of the first bipolar transistor, and an amplifiedsignal obtained by amplifying the radio frequency signal is output froma collector of the first bipolar transistor; a second bipolar transistorthat imitates operation of the first bipolar transistor when the radiofrequency signal is input to a base of the second bipolar transistor; afirst field effect transistor, wherein a power supply voltage issupplied to a drain of the first field effect transistor, a firstcontrol voltage is supplied to a gate of the first field effecttransistor, and a first bias current is output from a source of thefirst field effect transistor to the base of the first bipolartransistor and the base of the second bipolar transistor; and a firstresistor, wherein a second control voltage is supplied to a first end ofthe first resistor and a second end of the first resistor is connectedto a collector of the second bipolar transistor, and the first resistorgenerates a third control voltage at the second end of the firstresistor, the third control voltage corresponding to a collector currentof the second bipolar transistor.
 7. The power amplification moduleaccording to claim 6, wherein an emitter area of the second bipolartransistor is smaller than an emitter area of the first bipolartransistor.
 8. The power amplification module according to claim 6,further comprising: a second resistor, wherein a first end of the secondresistor is connected to the source of the first field effecttransistor, and a second end of the second resistor is connected to thebase of the first bipolar transistor; and a third resistor, wherein afirst end of the third resistor is connected to the source of the firstfield effect transistor, and a second end of the third resistor isconnected to the base of the second bipolar transistor; wherein theradio frequency signal is supplied to a node between the second end ofthe second resistor and the base of the first bipolar transistor, and toa node between the second end of the third resistor and the base of thesecond bipolar transistor.
 9. The power amplification module accordingto claim 6, further comprising: a fourth resistor, wherein a first endof the fourth resistor is connected to the source of the first fieldeffect transistor, and a second end of the fourth resistor is connectedto the base of the first bipolar transistor and the base of the secondbipolar transistor; wherein the radio frequency signal is supplied to anode between the second end of the fourth resistor, the base of thefirst bipolar transistor, and the base of the second bipolar transistor.10. The power amplification module according to claim 9, furthercomprising: a first capacitor, wherein the radio frequency signal isinput to the base of the first bipolar transistor and the base of thesecond bipolar transistor via the first capacitor.